The invention pertains to methods of bonding first and second masses to one another, and in particular embodiments, pertains to methods of bonding two similar materials together, as well as to methods of bonding physical vapor deposition target materials to backing plate materials.
There are numerous applications in which it is desired to bond a first mass to a second mass. One such application is in the bonding of physical vapor deposition targets (such as, for example, sputtering targets) to backing plates. The backing plates are configured to retain the targets in particular locations and orientations within pressure vapor deposition apparatuses.
Modern developments in physical vapor deposition methodologies have created increasingly stringent requirements for robust bonding between targets and backing plates. A diagrammatic view of a portion of an exemplary sputter deposition apparatus 10 is shown in FIG. 1. Apparatus 10 comprises a backing plate 12 having a sputtering target 14 bonded thereto. A semiconductive material wafer 16 is within apparatus 10 and provided to be spaced from target 14. Sputtered material 18 is displaced from target 14 and utilized to form a coating (not shown) over wafer 16.
Among the modern improvements in sputter design is an increase in the distance between target 14 and semiconductive material substrate 16. Such increase in distance can enable more directional sputtering to be achieved over features of substrate 16 than can be achieved when target 14 is close to substrate 16 by allowing atoms that are not moving perpendicular to substrate 16 to land on the sidewall of the sputtering chamber. Specifically, substrate 16 will frequently have vertical holes or slots (known as vias) with depths five times their width or more (i.e., having relatively high critical dimensions). It is difficult to sputter materials into vias having high critical dimensions unless there is a relatively long throw between a sputtering target and a substrate comprising the vias.
Although the longer throw creates advantages in coverage relative to shorter throw techniques, it also creates complications. One of such complications is caused by additional power utilized in long-throw technologies. The additional power can cause sputtering targets to get hotter than they had in older methods. Such heat can disrupt a bond formed between backing plate 12 and target 14. For instance, if target 14 is solder-bonded to backing plate 12, the heat developed during long-throw sputtering techniques can be sufficient to melt the solder bond and actually break target 14 free from backing plate 12. Accordingly, solder-bonding can be inappropriate for long-throw sputtering techniques.
A type of bonding which is generally able to withstand the high temperatures utilized in long-throw sputtering techniques is diffusion bonding, which is a bond formed by solid state diffusion of components from target 14 to backing plate 12 and/or vice versa. A difficulty in using diffusion bonding is that such typically comprises relatively high temperatures (300xc2x0 C. or more) to form the bond, and such temperatures can adversely affect target materials. Accordingly, it can be difficult to develop diffusion bonding processes for bonding physical vapor deposition targets to backing plates, and which further retain desirable properties of the physical vapor deposition targets. It would be desirable to develop such diffusion bonding processes.
In one aspect, the invention encompasses a method of bonding a first mass to a second mass. A first mass of first material and a second mass of second material are provided and joined in physical contact with one another. The first and second masses are then diffusion bonded to one another simultaneously with the development of grains of the second material in the second mass. The diffusion bonding comprises solid state diffusion between the first mass and the second mass. A predominate portion of the developed grains in the second material have a maximum dimension of less than 100 microns.
In another aspect, the invention encompasses a method of forming a physical vapor deposition target bonded to a backing plate. A target material and a backing plate material are joined in physical contact with one another. The target material and backing plate material both comprise aluminum. The joined target and backing plate materials are thermally treated under an atmosphere which is inert relative to forming oxides on the target and backing plate materials. The thermal treatment simultaneously diffusion bonds the target material to the backing plate material while recrystallizing grains in the target material. The diffusion bonding comprises solid state diffusion between the backing plate material and the target material to adhere the target material to the backing plate material with a bond strength of at least 5,000 pounds/inch2. A predominate portion of the grains developed in the target material are less than 100 microns in maximum dimension after the thermal treatment of the target and backing plate materials.